1. Field of the Invention
The invention disclosed herein relates to correlation of well logging data and, in particular, to correlation of bin logs derived from nuclear magnetic resonance (NMR) measurements to other logging data.
2. Description of the Related Art
In the field of geophysical exploration, a variety of technologies is employed for logging a well. The variety includes nuclear magnetic resonance (NMR), resistivity, saturation and others. Each technology has assets and liabilities. Accordingly, refinements to the various technologies are always in the works. For example, consider well logging using NMR.
In NMR well logging, an NMR probe is disposed into a wellbore. The NMR probe is used to conduct NMR measurements downhole. An improved technique for well logging with NMR involves use of the transverse relaxation time, T2, of media surrounding the NMR probe.
Fluid typing analyses of distributions of relaxation time, T, (e.g., the transverse relaxation time, T2, as well as the longitudinal relaxation time, T1) faces the problem of discriminating individual contributions of water and hydrocarbons, especially when signals from the water and hydrocarbons may not be easily discriminated from each other (that is, the signals are overlapping). For example, in the case of heavy oil, the overlap of the oil distribution with at least one of clay bound water and capillary bound water is very common. When there is no significant contrast in the diffusivity between the fluids, the fluid typing represent a difficult problem to solve, because in presence of a magnetic field gradient, the distribution of the transverse relaxation time, T2, for the various fluids present in the wellbore overlaps and cannot easily be cancelled. Other problems are encountered with regard to distributions of the diffusivity, D, that complicate fluid typing.
Therefore, what are needed are techniques for correlating logging information for at least the transverse relaxation time, T2, the longitudinal relaxation time, T1, and the diffusivity, D, with other types of logging data, such as those disclosed herein.